Mailings are subject to USPS procedures to verify correct preparation and postage payment. The mailer is responsible for correcting irregularities found in the mailing. If, at the acceptance unit, a mailing is found not to qualify for a Presorted First-Class Mail price or an automation First-Class Mail price, the mailer must either take corrective action or pay the full single-piece price. The return of such mailings to the mailer’s facility for any reworking is the mailer’s responsibility.

A mailer who pays the single-piece First-Class Mail price rather than correcting errors in a mailing paid with meter or precanceled stamps must pay the difference in cash at the window and present the copy of the cash receipt to the acceptance point before the mail may be released for processing. A mailer who makes the same choice for a mailing paid with a permit imprint must correct the postage statement presented with the mailing to show that postage is to be paid at the higher price.